Vehicle wiper control devices have been proposed in which wiping movement is controlled depending on the driving environment. More specifically, wiper control devices have been proposed in which wiping movement is automatically controlled based on the light levels (e.g., nighttime light and daytime light) and precipitation (e.g., rain, snow, sleet, etc.) affecting the vehicle.
For instance, Japanese Patent Publication No. 2002-211363A discloses such a system. At nighttime (i.e., lower exterior light levels), raindrops on the windshield can significantly impair the driver's ability to see because the raindrops diffusely reflect the light from the headlamps of approaching vehicles, etc. Thus, in the device of Japanese Patent Publication No. 2002-211363A, the exterior light level (i.e., whether it is daytime or nighttime) is determined based on a switching signal from a light switch. If it is nighttime (i.e., lower light levels), the wipers wipe more frequently than if it is daytime (i.e., higher light levels) for the same amount of raindrops on the windshield. Also, if the headlamps of the corresponding vehicle are in high beam mode, it is assumed that there are no approaching vehicles. Thus, even if low exterior light levels are detected (i.e., if it is nighttime), wiping frequency is reduced as compared with cases in which the headlamps are set in low beam mode.
However, these conventional wiper systems have certain problems. For instance, when a wiper is controlled based on a quantity of raindrops on the windshield, the sensitivity is adjusted if low light levels are detected so that wiping action is more likely to be initiated. When the vehicle enters a covered area of a road (e.g., when the vehicle enters a tunnel), rain stops hitting and sticking to the windshield, and it is desirable that the wiping be stopped as soon as possible. However, in this situation, the system will likely detect lower light levels, the sensitivity for controlling the wiper's wiping action is switched to lower-light sensitivity, and the wiper becomes more likely to perform wiping action. Thus, there can be a time delay before stopping the wiping action.
Also, when the vehicle exits a covered area and starts running on an uncovered road, raindrops will be detected on the windshield, and it becomes desirable to start wiping as soon as possible to improve the driver's view of the road. However, in this situation, the system will likely detect higher light levels, the sensitivity for controlling the wiper's wiping action is switched to higher-light sensitivity, and wiping action can be delayed.